Teletype communication system



. United States Patent 1 1 3,544,721

[72] lnventor John Van Geen 3,351,919 11/1967 Milford l79/2UX Sunnyvale, California 2,474,261 6/1949 Liebe 1 78/66( A) [2]] Appl. No. 618,945 3,414,828 12/ 1968 Westover 178/66X '1 d F 11.27 1967 lit ented 1, i970 Primary Examiner-Ralph slee [73] Assignee Stanf rd R h Institute Att0rneyr James Todorovic and Samuel Lindenberg Menlo Park, California a corporation of California [54] TELETYPE COMMUNICATION SYSTEM 5 Claims, 5 Drawing Figs. [52] U.S.Cl. 179/2, i ABSTRACT: A teletype communication system is provided 178/4 which converts teletype signals into signals shifted between [51] lnt.Cl. 11/06, two specified frequencies which represent characters being [50] Field ofsellth 179/2, transmitted, These are transmitted over a telephone line, At

2(C), 3,4, 2(DP); 178/58, 58.1,66, 66(A) the receiver, the received signals are converted into signals suitable for actuating a teleprinter. Acoustic coupling for Refermm Cited transmission and reception is employed between the terminal I UNITED STATES PATENTS apparatus and the telephone headsetsj Provision is made to 2,345,953 4/1944 Tolen 178/58(.l) eliminate noise effects p transmission and reception and 2,823,261 2/ 1 9S 8 Zipf 179/3 carrier ripple effects upon reception.

12 UPRIGHT CODE 30 BAND PASS DISCRIM FLIP To RESISTOR 4s MICROPHONE PREAHr R FILTER I cT. 2

14 18 mv. k 10 R20 22 CARRIER 1 28 CODE 34 32 DETECTOR 24 TRAP To RESISTOR 36 FROM CIRCUIT 1 iN EGRATOR-- TELEPHONE l 26 CENTRAL 17 VOLTS SOURCE TO FIG. 3

PLUG 64 HALF FULL 'DUPLEX 17 VOLT SOURCE 1 TELETYPE COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of telegraphy and more particularly to a system for an improved teletypewriter communication system.

2. Description of the Prior Art Teletypewriter communication systems which use the telephone lines for' coupling between stations have been developed and are now in use! For coupling the teletypewriter signals to be transmitted to the telephone lines, either direct coupling or acoustic coupling is used and for removing these signals from the telephone lines, usually inductive coupling techniques are employed. It is known that the telephone company makes headsets having different types of receivers which generate magnetic fields having different orientations and/or different strengths. Accordingly, a coupling coil for a teletypewriter system whichmay be operative with one receiver will not be operative with another receiver, or may require a considerable amount of adjustment before a usable signal can be obtained.

other problems which have continued to plague these types of systems are noise signals between the teletypewritei' and the frequency shift keyer which can cause erroneous frequency shift keying and ripple signals due to carrier signals on the telephone lines, which are not filterable and can operate to cause faulty operation of the teletypewriter at the receiver.

An object of this invention is the provision of teletypewriter terminal facilities whichcan couple to any type of telephone headset without requiring any physical contact or connection thereto.

Another object of the present invention is the provision of a teletyp'ew'riter terminal facility which substantially eliminates the effects of noise and ripple.

Still another object of the present invention is the provision ofinovel and improved teletypewriter terminal facilities.

SUMMARY The foregoing and other-objects of the invention are achieved by providingan acoustic coupling arrangement between the teletypewriter terminal facilities and the telephone receiver and transmitter. By way of example, a microphone is employed for 'picking up the output signals from the telephone transmitter and a loudspeaker is employed for driving a telephone receiver with frequency shift keying signals (FSK) generated by a teletypewriter terminal facility, in accordance with this invention. ln'order to minimize the effects of noise, which may. occur between the teletypewriter and the frequency shift keyer used to control the F SK oscillator, provision is made to drive the frequency shift keyer by a bistable circuit which respondsto the mark andspa'ce signals generated by the teletypewriter.

In order to minimize the effects of the ripple signals, after the signals received over thetelephone line have been passedthrough a discriminator, they are used to drive a bistable circuit which does not respond to ripple frequency signals but does respond to the frequency shift signals.

Other features of a teletypewriter terminal in accordance 'with this invention, is the provision of an option for half duplex operation whereby a teleprinter at a transmitter terminal can transmit messages and print out said messages simultaneously. Also provided is-a full duplex option whereby both teleprinter stations may act simultaneously as receivers and transmitters. I

Also, circuitry is provided whereby the transmitting and receiving circuits in accordance with this invention are usable with other electronic industry data equipment which is designated as EIA standard equipment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block schematic diagram of part of the equipment required at a teleprinter terminal for receiving signals from the telephone line;

FIG. 2 is a circuit diagram of other equipment required for driving a teleprinter with the signals provided by an arrangement in accordance with FIG. 1;

FIG. 3 is a schematic drawing of a teleprinter and its inputoutput plug which is shown for the purpose of providing an understanding of the operation of this invention;

FIG. 4 is a block schematic diagram of the transmitting portion of a teleprinter terminal in accordance with this invention; and

FIG. 5 is a block diagram illustrating an important utiliza- I tion of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to facilitate both the description of this invention and an understanding thereof, the explanation which follows commences with the premise that signals representative of characters have been transmitted by a teleprinter terminal in accordance with this invention, in the form of frequency shift keyed signals, henceforth referred to as FSK signals. These signals have been applied to a'telephone line acoustically in a manner which will be explained in connection with the transmitter of this system. A person who wishes to use a teleprinter terminal, in accordance with this invention, initiates a telephone call in the usual manner by dialing the telephone number of the receiving terminal. When the telephone is answered at the receiving terminal, he informs the party answerresponse is not'of too great significance.

. The output of the microphone is applied to a trap' circuit 16 which serves the function of shunting unwanted signal frequencies out of the signals which are applied to a preamplifier 18. In an embodiment of this invention which was built,

1 theunwanted frequency signals centered on l070-cycles per second, and these were removed by the trap circuit 16. The

preamplifier serves the usual function of' amplifying themicrophone signal output. The output of the preamplifier is applied to a bandpass filter 20, which serves the usual function of passing only those signals which have frequencies within the desired band. By way of example, in an embodiment of the invention which was built, the passband 'of the bandpass filter ranged approximately from 2000 cycles to 2250 cycles.

The output of the bandpass filter is amplified by amplifier 22. The output of amplifier 22 should comprise signals having one or the other of two frequencies which are the well known FSK signals. These signals are applied to a carrier detector circuit 24 which is a well known circuit for. providing an output signal when its input comprises signals'of one or the other of the two FSK signal frequencies. The output ofthe carrier detector is applied to an integrator circuit 26. This is a circuit, which is well known, which charges up a capacitor in the presence 'of an input signal.

The output of the amplifier is also applied .to the well known discriminator circuit which serves to pass only one or the other of the FSK signal frequencies. The output .of the discriminatoi' 28 may be connected through a switch 30 to directly drive a flip-flop circuit 32, when an "upright" code is desired. Alternatively, the output of the discriminator may be applied through the switch 30 to an inverter circuit 34, to drive the flip-flop circuit 32 with the output of the inverter circ'uit when an inverted code is used.

As is well known, the distinction between the upright code and the inverted code is that the mark and space signals in the upright code have respectively space and mark significance in the inverted code. The inverter circuit 34 inverts the received The'outputottheintegratorcircuit-ZG in'BlG',

thrcugh{a. resis tor;36;in FIG; 2 tothefof a'transistor 38. 1 The' ernfiuferofthetransissorflisconnected-to s source'ot;

potential140.;wliiclris on -theforder'ot i'lvolts. 'rhe collector; V f connected through ,a load resistor 42 ton plus potential some which msybe'on the order'otf +17 .voltsiA capscitordo is connected. betweenthe'basesndthe .e rnitter otthetrsnsistor as whereby a potential is sppli'edto: the base-of the transistor SQwhichcanrender it conductive in the .sbsencekot'other signalseilowever, infthe presence of a signaLofsuflicient amplitude applied from theiintegrator-26. l-(l-l0..1)to"the blase oftlietr'ansistor',transistor3 8.is.rendered nonconductivefl'his signsloccursiss-long ase'ithei'oi' the FSK -.-signslssrebein'g'received.-'

trsnsistor il'anditslassociatejdcomponents a H carrier-detecte'dby the detector circuit 24in FIG. 1-, thetrsnsistor- Slwould he conductive whereby adiode.

not respond to ripple signals; but can. only respond to .-.hsving amplitude of mark "and space signals which. are produced at' .theoutput of the. discriminator. Thus, the signals -thatare-applied-to the circuits which drive theltel'eprinter :signal decoder are clean sndcorrectbinary no.2 a s circuit'd ls mf'llustr'atingthe,usualmarlr-hold g 'rang'ernent inza'ceordance invention.-

; .lheoutput of ni -nop szIfliisp i sa s... the f transistor .47 througharssistorfidconnected in series with; ,diodeiSll; The emitter of the; mnfimtj through: s're'sistor 5 2.to thefn'egative potential source and I rates sothat,

were. there no 150 and s -7 rams meant m trmu'. mark.

ll-wouldb flop 32;.wh'ich is the .oneiof: the-1W9 outputs whichis con nected toathe resistordSJ-hus, in the absence o f any carrier: I

beinsdetectedtrsnsistor 4 7Jremains njthe m k cond tion.

I sndthetelepfrinterls notoperated. In

The ,output of transistor 41 is derived i'rorn emitter; its

amplifying transistor 58. The emitterof this transistoriscon-v the: collectorot transistorAIis, connected tothe potential. s ur 41 T emsi ir it represented y s4 which'hssitssnodelcohnectedto 1e ofthediode to the'collector of the transistornected to ground and thercolle ctor isconnected to a loadresistor to the negative operating potential source. The collector'is'iconn'ected' through'a' 'i'esistor, 62 to pin lot a female.

plug ,shown in FIG. 3,.wh ich is plugged into male'plug 66, which is connected to the teleprinter68. The-plug connectionsshown'in FIG. 3 -arethestandsrd ones forreeeivingout- 7 p tfwm r m v ns i putto a rel vant" swam" ne The erni. i'output of through a toa pin 3 c'ffthe'plug'fiflshown in FIG. 3.

A witnmnn no. 2-, has mo; positions, providing m 09'- tions, one; of these is designated'pas' thehall duplex whiehis the inthe drswing',and theother is It full duplex position as" previously explainedherein l'hehalf duplex optionis thejconventional one wherein a teleprinter atone location transmitssignslsto the teleprinter at the receiving location, and 'simultsn'eously typ es' the message being transmitted. The teleprint'er 'st-the receivinglocation, after all r r signals. have. been received csn thenv transmit back to the y original transmitting location. The. h llduplex optionis one wherein" the teleprinter terminals can both receive andtrsns mit signals simultaneously.

' Referring nowtoIl-lG; 3, terminals, 1, 2 and 3 osmium-1 relay 98,which is shown inFlG. 4'. The inverter relay 98 in the V enable the transmission of the msrlespace signal in the-upright code. in, the other-position. he l'signals are inverted by. means The teleprinter-gener ates mark Sare' the ones to which the out put of the teleprinter 68 are applied, which occur upon theactuation of any of the keys of the teleprinter. Terminals and the ones to which the input signals received over the telephone lines are applied, for actuating the printing units of the teleprinter forprinting' out the message received. Terminal 7 {is connected by a lead directly to terminal 5, when it is desired touse' the j 'systern with a teleprinter. When his desired to use BIA standard equipment the lead connecting terminals 8 and 5 isrernoved,'thus allowing pin 2 tube independently driven. lerrninal 8. is connected through a resistor 80, shown in HG Z tothej'PITvoItpotentialsourceJ V v 1 The two terminals. and 5': in FIG. "3,which provide the.

marltand space output signals'tepifesentative oi the key-which also through a 'resistor 88 connected in series a diode 90,

to the use r atransistor llz Transistor 92-; haslits emitter 94 l i "connected'to' negative potential source lts collector is connected the'positive potential source 44.*The emitter of transistor is connected through a resistor 96 to an inverter with. in FIG. 4, will ofthe inverter 100.-

'l'heoutputreceived'directly irons the' teleprinter or the out 1 i ,put received from the inverter 100 is applied .to' drive the flipflop-1 02. space signal anvesime flip-flop to a set state vfrom which it is returned to, a reset state bythe mark signal.

The set output of the flip-flop is applied to drive a fre'quency shiftkeyer circuit 104. 'lhis'fre'quencyshift keyer circuitis v ;,weu knowncircuitry, which is used tod'rivesn oscillator 106 tofprovide as anoutput' onefor the other of two-oscillation frequencies as determinedby the mark and spaceinputs to the 'fl ip flop"l0 2. By way. of 'illus'tratiomand not to serve asa limitation upon the inventionflwo"frequencieswhich-were employed as" the respective and space representativei270 .cycles'per sfeeonds'nd i010 cycles per r The flip flop circuit Hi4 is another important feature of this invention, since 'it ensures that the frequency shift keyer is driven'in responseto only thejmsrlt' and space signslswhich are provided by {the teleprinter andnot by'any noise signals.

By reason of the flip-flopcircuit. required amplitude driving 'ernitter is connected through a resistor 56 to the base. of an generated by the 'telepnnter and the intervening circuits to the -FSK driver are substantially eliminated. a a The output of the oscillator circuit 106 is appliedto a loudspeaker 110. The transmitterin of the usual te lephone'hesdset 114 is placed adjacentlthe loudspeaker to be-driven vthereby. A telephone headset 114 isconnected'to the usual telephone central I16, and sends out thesignsls that it receives to the telephone central. r

aneapplied via pins 4 an s and-specifically over pin 5 (the.

92. Output is taken from the emitter of this transistor, and

-;.through resis'tor 9a is applied to theinverter relay 96' in no. 2 A and alto via switch 72-, whenin itshalf duplex position, to a re-' "sistor l18which is connected in'series with a 120. The

diode in turn is connected'to the base of transistor 47 It should be recalled that the transistor 47 is used to apply. incoming mark-space teleprinter code signalswto: the local teleprlnter. 'Thereformin the-half duplex mode, the signals which are produced by-the local teleprinter are both transmitted and are returned todiivethe local teleprinter to P plug are theones which are used" forElA-standsrd data 7. using the teleprinten 'd space and,

uoe an indication of the data which is being transmitted type described has an output loudspeaker 122 and "an input microphone 124. These are acoustically coupled to a telephone headset 126. The headset 126 is connected, in well known fashion, through telephone central, 128, to another headset 130. The telephone headset 130 is acoustically coupled, via a receiving microphone 132, and transmitting loudspeaker 134, to the teleprinter terminal 136. The teleprinter terminal 136 can be used to address or as a data input device for a a computer 138. The teleprinter terminal 136 can also serve as an output device for the computer, and the information received from the computer can be then sent back to, the. teleprinter terminal 120. Thus, there isprovided a means for acoustically communicating with an receiving data from a computer through the telephone lines, by means of this in vention.

There has accordingly been described and shown herein a novel and useful teleprinter terminal arrangement which, by the use of acoustic coupling techniques avoids the problems of coupling to different types of telephone headset arrangements. Also, the system, in accordance with this invention,

7 provides a circuit arrangement whereby the effects of locally generated noise on transmission are substantially eliminated as well as the effects of carrier ripple which can cause errors in the receiving equipment.

By virtue of the all acoustic" coupling of a teleprinter terminal to a telephone headset, afforded by the present invention, teleprinter terminals may be made portable to enable ready communication, from any'telephone location to any shift oscillations responsive thereto; and I l acoustictransducer means for converting the output of said frequency shift oscillator means to acoustical signals suitable for application to a telephone headset'for transmission over a'telephone circuit. v

' 2. A teleprinter terminal as recited in claim 1 wherein there is includedmeans for receiving the frequency shift oscillations which are transmitted over the telephone line, a single flipflop for converting-said received signals to a serial train of binary signals, and teleprinter fne'ans for utilizing'said binary signals. a

3. in a teleprinter terminal of the type wherein teleprinter signals are applied to the transmitter of a telephone headset for transmission over telephone lines, and the transmitted signals are received from the receiver ofa telephone headset and are thereafter applied to the teleprinter means, the imfirst transistor means for applying signals generated by said teleprintermeans to said telephone headset transmitter; second transistormeans. for applying signals from said telephone headset microphone to said teleprinter means;

switch means having an open ,and a closed position, for

respectively providing a full and half duplex option; and means connecting the switch means when in its closed position between the output of said first transistor meansand the input to said second transistor'means. 4. Apparatus as recitedin claim 3 w'herein there is included in saidmeans for coupling the signals from said telephone headset microphone to said teleprinter means; microphone means for acoustically coupling to said telephone headset microphone; flip-flop means having its output connected to said second transistor means; inverter means having an input and an output connected to saidflip-flop means input;'and

' switch means having a first position for connecting said other telephone location. There is afforded, by this invention,

a means of communication from a portable teleprinter terminal to a centrally located teleprinter terminal which can include a computer facility for which the teleprinter serves as an input-output device. As a result, inquiries may be addressed to a computer from any telephone location, no matter-how remote, and the answer thereto is received and typed-out at the portable teleprinter tenninal.

lclaim: v

l. A teleprinter terminal having a teleprinter for generating mark-space teleprinter signals desired to be transmitted "and for responding to received mark-space teleprinter signals,-said terminal including a single flip-flop to which all of said markspace teleprinter signals to be transmitted are applied for generating at its output a serial train of binary signals representative of said mark-space signals;

a frequency shift oscillator means to whichthe output of said single flip-flop is applied for generating frequency microphone means output to said flip-flop means input and a second position for connecting said microphone means output E to saidinverter-means input for respectively providing upright i having a'first position for connecting said first transistor which said frequency shift keying oscillatormeans is applied means output to said flip-flop means input and a second position for connecting said first transistor means output to said inverter means input for respectively providing an upright and inverted code option; frequency shift keying oscillator means; means for driving said frequency shift keying oscillator means with'said flip-flop means output;v and loudspeaker means to for acoustically applying signals to said telephone transmitter. 

